During the last decade, the incidence of breast cancer in women born since the mid-1940's has been increasing in Washington State. We propose to conduct a case-control study to examine possible reasons for this increase. We will focus on exposures that have themselves changed during this time period, or exposures that distinguish these cohorts from their predecessors. All white female residents of King, Pierce, and Snohomish Counties born after 1949 and diagnosed as having breast cancer during the period Jan. 1984 to Dec. 1988 will be identified and invited to participate in the study. The identification of the approximately 400 such women will be through the rapid reporting network of the Cancer Surveillance System (CSS), a population-based tumor registry that has served the area since 1974. Female residents of these counties, matched to the cases (one to one) on age (five-year groups) and geographic location (county), will be selected by a random digit dialing method based on the Waksberg procedure for survey sampling. Interviews will take place in the study subject's home (or at another place of their choice). Because a) a history of induced abortion is much more common in women who have spent their reproductive years in the recent era when this procedure has been legal than it has been in women of earlier generations; and b) several prior studies have produced results suggesting an increased risk of breast cancer associated with a history of induced abortions, particularly if performed prior to a woman's first full-term pregnancy, we will devote special attention to this variable. Thus, the interview will elicit a detailed reproductive history in order to obtain information on the number of abortions (induced and spontaneous), their timing with respect to other pregnancies and menarche, contraceptive methods that followed the abortions, etc. Irrespective of prior abortions, a detailed contraceptive history will be obtained, so that we may be able to shed some light on the possible association between oral contraceptive use early in reproductive life and the incidence of breast cancer.